Libertarians fall into two distinct groups: strict libertarians like Rand Paul and classical liberals such as myself. “Classical liberal” is not a term that rolls off of the tongue. Consequently, “libertarian” is the choice term in popular discourse when discussing policies that favor limited government. Libertarians of all stripes oppose President Obama’s endless attacks on market institutions and the rich. The umbrella term comfortably embraces both strands of libertarian theory vis-à-vis a common intellectual foe.

It is important to understand the differences in views between the strong libertarian and classical liberal position. Serious hard-line libertarian thinkers include Murray Rothbard and Karl Hess. Rothbard believes nonaggression is the sole requirement of a just social order. For Hess, “libertarianism is the view that each man is the absolute owner of his life, to use and dispose of as he sees fit.” There are large kernels of truth in both propositions. It is quite impossible to see how any social order could be maintained if there were no limitations against the use, or threatened use, of force to enslave or butcher other people, which Hess’s proposition of absolute self-ownership strongly counteracts.

Yet the overarching question is how does a group of people move from the Hobbesian “war of all against all” toward a peaceful society? Hess claims that stable institutions are created by “voluntary association and cooperation.” Again, strong libertarians are on solid ground in defending (most) private contracts against government interference, which is why Lochner v. New York (1905), reviled as it is by most constitutional thinkers, was right in striking down New York’s sixty hours per week maximum labor statute. Yet the hard-line libertarian position badly misfires in assuming that any set of voluntary contracts can solve the far larger problem of social order, which, as Rothbard notes, in practice requires each and every citizen to relinquish the use force against all others. Voluntary cooperation cannot secure unanimous consent, because the one violent holdout could upset the peace and tranquility of all others.

The sad experience of history is that high transaction costs and nonstop opportunism wreck the widespread voluntary effort to create a grand social alliance to limit the use of force. Society needs a coercive mechanism strong enough to keep defectors in line, but fair enough to command the allegiance of individuals, who must share the costs of creating that larger and mutually beneficial social order. The social contract that Locke said brought individuals out of the state of nature was one such device. The want of individual consent was displaced by a consciously designed substantive program to protect both liberty and property in ways that left all members of society better off than they were in the state of nature. Only constrained coercion can overcome the holdout problems needed to implement any principle of nonaggression.

The flat tax is preferred because it reduces private incentives to game the tax system and, likewise, the ability of government officials to unfairly target their opponents. The optimal theory of taxation minimizes the distortions created by the need to fund the government activities that maintain public order and supply infrastructure. The classical liberal thus agrees with the hard-line libertarian that progressive taxation, with its endless loopholes, is unsustainable in the long run. At the same time, the classical liberal finds it incomprehensible that anyone would want to condemn all taxes as government theft from a hapless citizenry. The hard-line libertarian’s blanket condemnation of taxes as theft means that he can add nothing to the discussion of which tax should be preferred and why. The classical liberal has a lot to say on that subject against both the hard-line libertarian and the modern progressive.